High-frequency heating apparatus



June 20, 1950 M. F. DAVIS HIGH-FREQUENCY HEATING APPARATUS Filed Sept. 1, 1948 Inventor: Maur-nce F Davis,

@wm His Attorney.

Patented June 20, 1950 HIGH-FREQUEN CY HEATING APPARATUS Maurice F. Davis, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application September 1, 1948, Serial No. 47,173

' Claims. (01. 219-47) apparatus, more particularly to high frequency apparatus employing electrodes for the continuous heating of elongated material, and has for its object simple and reliable high frequency heating apparatus provided with improved means for preventing electric arcing and corona discharge from the electrodes.

My invention is useful in the heating of materials which when being heated evolve an appreciable amount of vapor more conductive electrically than air. Such vapor evolving conditions are found in the heating for drying or curing purposes of various elongated materials which are passed continuously in the form of strips, threads, or cords between spaced electrodes supplied with high frequency energy at a suitable voltage. Such materials are textiles, rayon, rubber, plastics, paper and the like.

It has been found that the water or other vapor evolved in the drying of the material by passing it continuously between two electrodes induces arcing between the two electrodes and between the electrodes and the material, and corona discharges from the electrodes. These efiects are undesirable because of the resulting power loss which decreases the efficiency and effectiveness of the heating apparatus and various means have been employed to counteract these effects. One apparatus for this purpose is disclosed in Patent No. 2,473,251 granted to Eugene T. Hsu on June 14, 1949, which is assigned to the assignee of the present invention.

I have found, however, that when an apparatus of the type disclosed in that application is completely enclosed during operation that the water or other vapor produced by the action of the dielectric heat upon the moisture contained in the material is detrimental to the operation of the apparatus. When this vapor gets between an electrode and the quartz or Pyrex glass tube which surrounds it in one form of that apparatus, it has a tendency to produce very minute or pin-point arcing between the quartz or Pyrex glass tube and the material being dried, to the detriment of the material. I have found that by sealing the ends of the electrodes and their corresponding tubes so that there is a dry air space between electrode and tube that the pin-point arcing is eliminated.

In carrying out m invention. in one form, I surround elongated cylindrically shaped electrodes with concentric tube shaped members of quartz or Pyrex glass of substantially larger diameter. The ends of the surrounding quartz or glass tubes are tapered so that the internal diameter at the ends is approximately the same as the outside diameter of the electrodes. The ends of the electrodes and surrounding tubes are sealed by suitable means to create a dead air space between the two and prevent outside atmosphere from entering that space.

For a more complete understanding of my invention, reference should be had to the accompanying drawing, Fig. 1 of which is a fragmentary view, in perspective, of high frequency heating apparatus embodying my invention; Fig. 2 is an enlarged view of two of the electrodes shown in Fig. l; and Fig. 3 is a sectional view showing the details of the seal between an electrode and its surrounding quartz or Pyrex tube.

I have shown in Fig. 1 one form of my invention as applied to the heating for drying purposes of warp threads on a slasher. In passing through the slasher, the plurality of parallel warp threads indicated as a band or strip I are passed through a suitable container (not shown) containing a, sizing material, such as water, with a small amount of gelatin, after which the warp is passed through rolls (not shown) for the removal of the excess liquid and then heated in m heating apparatus to dry on the remaining liquid.

For purposes of simplification, I have shown the warp threads I as being passed between two rollers, 2 and 3. It will be understood that suitable driving means (not shown) is provided for one of the rollers for winding the warp on that roller and drawing it off the other roller. The warp threads may be rayon, cotton, Or other like material.

In accordance with my invention, I provide upper and lower groups of electrodes 4 and 5 adjacent respectively the upper and lower sides of the warp, although preferably the spacing is suflicient to prevent the touching of the electrodes by the warp threads and the deposit thereby of sizing material on the electrodes. The electrodes in each group are arranged in aligned coplanar equidistant parallel relation and extending cross wise with respect to the warp and the electrodes of one group are in staggered relation with respect to the electrodes of the other group. As shown, the upper group of seven electrodes 4 are supported on electrically conducting angle members 6 which, in turn, are supported by plate 1 through four electrically insulating corner posts 8. The lower group of six electrodes 5 is sup-- ported in parallel relation with the upper group directly by electrically conducting plate 9. The electrodes of each group are, in addition, electrode in a quartz or Pyrex glass tube It, shown in detail in Figs. 2 and 3. The electrode itself is an inner tube II, as shown in Fig. 3, made of a suitable conductive material, such as copper,- which tube is mounted inside of the outer insulation tube I0. The internal diameter of outer warp I or other material into the heating apparatus.

The efficiency of my heating apparatus is increased by the staggered relation of the electrodes of the upper and lower groups. In this arrangement, the electric field appears between each bottom electrode and the two top electrodes between which the bottom electrode is positioned and this electric field extends substantially along the length of the warp so as substantially to surround the warp throughout the length of the heating apparatus.

tube I0 is substantially larger than innerv conductive tube II for most of the length so that a peripheral space is provided between them."

The ends of the outer insulating tube II] are tapered so that the internal diameter at the extreme ends is slightly greater than the diameter of inner conducting tube I I.

Outer tube In is shorter by a small amount than inner tube I I so that when the latter is installed inside the former, it projects slightly at both ends.

On the shoulder thus formed at each end of the electrode assembly is a washer I2 of neoprene or other suitable material to seal the space between outer tube It and inner tube II and prevent the entry of outside atmosphere into that space. The two electrically conducting members I3 and I4 of the electrode assembly, shown best in Fig. 3, are counter-sunk to shield the sealing washer I2 from the electric field between the electrodes and between the electrodes and ground. Inner electrode tube II has a threaded projection at both ends for connection to corresponding threaded portions on members I3 and I4. These threads also provide the means by which sealing washers I2 are compressedagainst tube III and electrode II to provide a gas-tight, effective seal between tube I0 and electrode :I I.

I have found that sealing the space between tube Ill andelectrode II prevents pin-point arcing between tube Ill and warp I, even though the atmosphere surrounding tube I0 is heavily vapor laden.

Vertical conducting members I5 support and connect one end of the electrode assemblies to angle member 6 or plate 9 as the case may be. Member I5 has a hole through one end throughwhich the threaded portion of electrode I-I pro-. Jects and is secured by two nuts I6 and II. The other end of member I5 is threaded and is fastenecl to channel 6 or plate 9 by nuts I8 and I9.

he upper and lower ends respectively of member It are also threaded and are fastened to angle member 6 or plate 9 by nuts and 2I.

Preferably, as shown in the drawing,'electrode groups 4 and 5 are somewhat longer than the width of the warp I to reduce the intensity of the electric field near the ends of the electrodes in order to reduce the possibility of arcing and corona discharge from the ends of the electrode assemblies. Furthermore, the ventilation carrying away the vapors is more eflicient at the exposed ends of the electrode assemblies s that arcing and corona discharge are not likely to occur at the ends. Preferably, forced ventilation by a fan (not shown) is provided for the enclosure in which my heating apparatus operates.

End members I4 supporting one end of the electrodes are shaped in the form of a circular sector, as shown in Fig. 2, to facilitate threading of the In order to prevent interference with radio communication by the high frequency waves '15 radiated from the heating apparatus the apparatus preferably is enclosed in a field or enclosure (not shown) made of electrically conducting material and provided with a slot at each end for the passage of warp I.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

' What I claim as new and desire to secure by Letters Patent of the United States is:

l. A high frequency heater for drying material impregnated with a vaporizable liquid, comprising two electrodes of electrically conducting material, electric connections for supplying'high frequency current to said electrodes, means for supporting the material to be dried adjacent said electrodes whereby said material is heated and the liquid driven off in the form of vapor, an enclosing member of electrically insulating mate rial surrounding at least one of said electrodes in spaced relation therewith, said enclosing member being interposed between the two electrodes, and vapor tight sealing means confining the atmosphere between said electrode and said enclosing member and preventing outside atmosphere from entering the space between said electrode and said enclosing member. I

2. A high frequency heater for drying material impregnated with a vaporizable liquid comprising two elongated electrodes made of electrically conducting material, electric connections for supplying high frequency current to said electrodes, means for passing the material to be driedbetween said electrodes whereby said material is heated and the liquid driven off in the form of vapor, an outer tube of electrically insulating material surrounding each of said electrodes, electrically insulating spacing means for securing each of said outer tubes in spaced relation with its said electrode, and vapor tight sealing means confining the atmosphere between each ofsaid tubes and its said electrode and preventing outside atmosphere from entering the space between each of said tubes and its said electrode.

3. A high frequency heater for drying elon gated material impregnated with a vaporizable liquid comprising two cylindrical electrodes made of electrically conducting material, electric connections for supplying high frequency current to said electrodes, means for passing the material to be dried between said electrodes whereby'said material is heated and the liquid driven ofi in the form of vapor, an outer tube of vitreous electrically insulating material having a high'dielectric constant surrounding each of said electrodes, each'of said'outer tubes having an internal diameter substantially larger than the diameter of its said electrode for most of the length, with the ends of said tubes tapered so that the internal diameter at said ends is such that said electrodes are supported in spaced concentric relation within said tubes, and electrically insulating vapor tight sealing means preventing outside atmosphere from entering and confining the atmosphere between each of said tubes and its said electrode.

4. A high frequency heater for drying material impregnated with a vaporizable liquid comprising, two groups of electrodes positioned in substantially parallel spaced apart cooperative relation and defining therebetween a space for the passage of material to be dried, each such group including a plurality of elongated electrodes positioned in parallel spaced apart substantially coplanar relation, each of the individual electrodes of one of said groups having a curved member attached to one end to facilitate threading the material to be dried between said two groups of electrodes, electric connections for supplying high frequency current to said electrodes, means for passing the material to be dried between said two groups of electrodes whereby said material is heated and the liquid driven 01f in the form of vapor, a plurality of individual enclosing members of electrically insulating material surrounding said electrodes in spaced relation therewith, and vapor tight sealing means confining the atmosphere between said electrodes and said en closing members and preventing outside atmosphere from entering the spaces between said electrodes and said enclosing members.

5. A high frequency heating apparatus for the drying of continuously moving strip material impregnated with a vaporizable liquid comprising, two groups of electrodes positioned in parallel spaced apart relation and defining therebetween a space for the passage of material to be dried, each of such groups having a plurality of elongated electrodes positioned in aligned equidistant parallel spaced apart coplanar relation at right angles to said passage, the spacing of the adjacent electrodes in each group being equal to the spacing of those in the other group and the two groups being positioned in staggared relation on opposite sides of said material passage space whereby each intermediate electrode of each group is substantially equidistant from the two adjacent electrodes of the opposite group and in current conducting relation therewith, a plurality of curved conductive members attached respectively to corresponding ends of the individual electrodes of one of said groups to facilitate the threading of the material to be dried between said two groups of electrodes, electric connections including said curved members for supplying high frequency current to said electrodes, means for passing the material to be dried in substantially parallel relation between the two groups of electrodes whereby said material is heated and the liquid driven off in the form of vapor, a separate outer tube of electrically insulating material surrounding each of said electrodes, electrically insulating spacing means for securing each of said outer tubes in spaced relation with its electrode, and vapor tight sealing means confining the atmosphere between each of said tubes and its electrode and preventing outside atmosphere from entering the space between each of said tubes and its electrode.

MAURICE F. DAVIS.

REFERENCES CITED The following references are of record in th file of this patent:

UNTTED STATES PATENTS Number Name Date 2,163,898 Van Der Lande June 27, 1939 2,288,269 Crandell June 30, 1942 2,291,807 Hart Aug. 4, 1942 2,360,108 Christie Oct. 10, 1944 

